1. Field of the Invention
The present invention relates to semiconductor devices, and in particular to a semiconductor device of the resin-sealed type formed with a lead frame.
2. Description of Related Art
As an example of semiconductor devices of a resin-sealed type that are formed with a lead frame, those of a QFP (Quad Flat Package) type are conventionally known. Generally, in QFP type semiconductor devices, by narrowing the width of the inner lead portions (lead terminals) of the lead frame, larger number of pins and finer pitches are achieved so as to cope with higher degrees of integration in semiconductor elements.
However, since there is a limit to the formation of the width of inner lead portions (lead terminals), in a case where the number of inner lead portions (lead terminals) is increased so as to cope with an increased number of pins, it is necessary to enlarge the size of the lead frame itself. And as the lead frame is enlarged, the distances between electrode pads of a semiconductor chip and the inner lead portions corresponding thereto are lengthened. Accordingly, there arises a disadvantage that the bonding wires that electrically connect the electrode pads and the inner lead portions are lengthened.
Here, if the lengths of the bonding wires exceed a predetermined length, so-called wire sweep takes place in which the bonding wires are deformed in the flow direction of sealing resin during the process of resin-sealing the semiconductor chip with the sealing resin. As a result, there arises a disadvantage that a short-circuit occurs owing to the mutual contact of adjacent bonding wires. Generally, in a semiconductor device of a QFP type, of all the bonding wires, those at the corners of the semiconductor chip are longest, and therefore the occurrence of the aforementioned wire sweep is noticeable at the corners of the semiconductor device.
In this connection, there is conventionally known a QFP type semiconductor device capable of suppressing the wire sweep at the corners thereof. A semiconductor device of this type is described, for example, in Japanese Unexamined Patent Application Publication (JP-A) No. H10-116953. This publication discloses a QFP type semiconductor device in which the inner lead portions connected to the electrode pads at the corners of the semiconductor chip are arranged closer to the semiconductor chip than the adjacent inner lead portions are. In the conventional semiconductor devices structured in this manner, it is possible to prevent the bonding wires at the corners from becoming longer than the rest, and therefore it is possible to suppress the wire sweep at the corners of the semiconductor device.
However, in the conventional semiconductor device disclosed in the aforementioned publication JP-A No. H10-116953, in a case where the number of lead terminals (inner lead portions) is further increased so as to cope with an even larger number of pins, the lead frame becomes even larger, and therefore there arises a disadvantage that the bonding wires except those at the corners of the semiconductor device become longer than a predetermined length. Thus, with the structure described above, the semiconductor device, though capable of suppressing the wire sweep at the corners thereof, yet has a disadvantage that the wire sweep still occurs at any part of the device other than the corners. Accordingly, in a case where even larger numbers of pins and even finer pitches are to be coped with, the semiconductor device in JP-A No. H10-116953 raises a problem of lowering the manufacturing yield and reliability of the semiconductor device due to a short-circuit between bonding wires resulting from the wire sweep. Incidentally, it is difficult to overcome the above-mentioned disadvantages and problems by changing the conditions of the resin-sealing process or changing the material of the bonding wires.